This Mechanical 7-Segment Display Was Built Using LEGO Technic Parts

Vaclav Krejci, who goes by “upir” on YouTube, is a big fan of seven-segment displays — as are we all. Over the years, he has built many projects that either make use of seven-segment displays or that are, themselves, unique seven-segment displays. Most of them use some source of illumination for the segments, but seven-segment displays can also be mechanical. However, those mechanisms can become very complex and so Krejci turned to LEGO Technic when building a mechanical seven-segment display in his most recent video.

We have seen mechanical seven-segment displays that use extremely clever mechanisms to reduce the number of necessary actuators — including one that cycles through all ten digits with just a single hand-cranked input shaft. But Krejci kept things simple and used one servo motor for each segment. Because this is a LEGO build, those aren’t your typical micro servos. Instead, Krejci used Geekservo models that are compatible with LEGO bricks. But aside from the unique form factor, they operate just like normal servo motors.

With actuators ready to go, Krejci designed the rest of the display. It shows each segment as a handful of LEGO Technic shafts that poke through holes in a faceplate. Each set of shafts attach to a rack-and-pinion gear mechanism actuated by one of the servo motors. When extended, the shafts protrude from the faceplate and their contrasting color (black on yellow) is very visible. When retracted, they are far enough inside their holes that they are only visible if you look at them straight-on. By extending just the corresponding segments, they can form any digit.

Krejci came up with two ways to control the displays for the video demonstration. The first is a manual servo control board that has eight potentiometer knobs tied to the eight servo motor connections. It lets Krejci set the position of each segment with the twist of a knob.

But that isn’t very useful for actually displaying information, so Krejci also built a version controlled by an Arduino UNO board. That automatically sets the positions of the segments programmatically, so Krejci can set it to cycle through digits, to display digits at random, or to display digits sent by a connected computer over serial.

It could, for example, show the value from a sensor connected to the Arduino — just like any other seven-segment display, which is why it is so cool.